Noiseless explosive rivet



Sept. 24, 1957 R. J. MILLER NOISELESS EXPLOSIVE RIVET Filed Aug. 11, 1955 FIG. 2

FIG. 1

FIG. 4

FIG:3

FIG. 6 g

FIG. 5

ATTORNEY United States Patent NOISELESS EXPLGSIVE: RIVET Ross Jay Miller, Pitman, N. .L, assignor to E. I. du. Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application August 11, 1953, Serial: No. 3.7.3,.629'

4 Claims. (Cl. 85-40) or other material which are in positions difficul't of access 5 from one side. Such rivets have been used, for example, in the fastening of skin to airplane frames, inthe assembly of truck and bus bodies, refrigerators, and the like, and in repair work. In practice it is customary to operate in the following manner in the application of rivets of this type. A rivet containing anexplosive charge in a recess in the shank is introduced into a hole formed through each of the two or more plates to be joined; heat is applied to the head end, and the explosive charge is brought to explosion thereby. The explosion of the explosive charge expands the shank of the rivet to cause it to hold the plates ofmetal firmly together.

Rivets of the explosion type have been particularly effective where thin plates or other small pieces-were tobe joined by small rivets, that is, for example, rivets not exceeding approximately in.v in shank diameter, be cause the noise produced by their use, while appreciable, could be tolerated. When, however, it has been desired to use rivets of larger size for the riveting of larger pieces, it has been found to be impracticable because the noise produced as the rivets exploded exceeded the limit of human endurance.

When attempts have been made to prevent the immediate escape of the gases produced by the explosion of the explosive charge of explosive rivets and thereby to deaden the noise of the explosion, as'by screwing a plug into the open end of the rivet shank orby screwing acap on the shank end of the rivet, for example, failure has resulted because the pressure produced by the confined gases has been. suflicient to strip the screwthreads and thus to dislodge the plug or cap and propel said plug or cap like a projectile.

An object of the present invention is an: explosive rivet which isessentially noiseless when exploded. A further object is such a rivet which. doesnot present the hazard of forming flying missiles. A stillfurther-object is such a rivet which may contain: a relatively large charge of explosive. A stillfurther object is an explosive rivet which does not blast opposite structures: during its expansion. Additional objects will be disclosed as the invention is described more fully hereinafter.

I have found that the foregoing objects are accomplished in a satisfactory manner when I provide anexplosive rivet having a head, a shank, a recesswithin the shank opening at the end opposite the head, and-an. eX- plosive charge within the recess, with an and closure comprising a metal plug having an irregular surface positioned entirely withinv the recess. near the opening thereof, the opening having been constrictedto reduce: its;diam

eter to less than the diameter of the plug. A desirable "ice consequence of compressing the end of the shank to reduce the diameter of the opening is that at, least a portion of the irregular surface of the plug is imbedded into the shank, thus providing a firmer grip.

In order to describe the invention more clearly. reference is made to the accompanying drawings, which are not to be taken as limiting in any way. Figure 1 shows an explosive rivet in position for riveting together two metal sheets. Figure 2 shows the same rivet after explosion. Figures 3 to 6 show plugs suitable for use in the rivet of Figure 1, the surfaces of the plugs being made irregular in various ways.

In Figure l, the shank 2 of the rivet is inserted through the drill hole in the two metal sheets 5 and 6 which are to be joined together. When in place, the head- 1 of the rivet rests firmly against the nearest metal sheet. Within the recess or cavity 3 in the shank of the rivet is a small charge of a detonating explosive 4. At the base of explosive charge 4 is a small serrated cylindrical plug- 7, the base of the cylinder abutting the base of the explosive charge and the serrated portion of theycylinder being adjacent to the smooth walls of the cylindrical recess. At the lower portion of the serrated plug; the shank of the rivet is narrowed by a constriction 8 which serves; to hold plug 7 in position and which grips the lower serrations of the plug, but which does not entirely close off the end of the rivet shank. In Figure 2 the walls of the rivet shank are shown as they appear after they have been caused to bulge by the detonation of the explosive charge, thus fastening plates 5 and 6- firmly'together by means of the expansion of cavity 3.

Figures 3, 4, 5, and 6 show various; additional forms f plugs of irregular surface which are suitable for use inthe explosive rivets described; Figure 3 shows a cylindrical plug which is threaded on its cylindrical surface. Figure 4 shows a cylindrical plug in which a plurality of notches have been cut in the cylindrical. surface. Figure 5 shows a plug particularly suited for usev in small rivets in which. the whole, cylindrical surface is pebbled. Figure 6 shows: still another form of serrated plug.

When rivets of the type described are firedby' application of heat to the rivet head, a sharp metallic click is heard instead of the loud report produced. byrivetsmade heretofore. Even rivets as: large as /8 in. in diameter make no greater noise than this metallic click. When 400 brass rivets 7 in. indiameter formed with severely restricted terminal closures in accordance with my invention were fired experimentally under normal factory riveting conditions, no noise beyond the click was made in any case, to the great astonishment of the-riveters, and rivet performance was satisfactory in every respect. Expansions were normal, without splitting or shattering of the. rivet shanks or emission of projectiles.

The noise reduction is believed-entirely due tothe fact that the gases produced by the decomposition of the explosive charge are not permitted to rush out instantly, but instead, are trapped Within the rivet. It is not essential that the closure of the present invention form a perfect gas seal, since the slow escape of the gases under pressure within the shank of the rivet will not produce noise.

A striking demonstration of the effectiveness of the present closure in restricting the escape of gases from the rivet consists in immersing in water a. rivet which has just been fired. In most cases, bubbles will form at the exit point of the narrowed end of the shank of the. rivet. The. bubbles are small, form slowly, and continue to rise from the immersed. rivet for a number-of minutes or. even for several hours. 1 e

Whena rivet producedv in accordance, with. the present invention is fired with the shank end in water, an. initial surge of gas may flow from the shank, but other than this, no disturbance or shock is produced.

While various forms of metal plugs having roughened surfaces are suitable for use in my invention, I prefer to use substantially cylindrical plugs, since these are easier to engage or infix in the cylindrical wall by means of the constriction at the base of the rivet shank than are plugs of spherical shape or of square cross-section, for example, although it is possible to use the latter types when adequate closure means are provided.

In addition to the plug surfaces shown in Figures 3 to 6, many other types of irregular surfaces may also be used. The surfaces may be corrugated, wrinkled, scored, grooved, ribbed, toothed, knurled, or the like. A notched plug such as is shown in Figure 4 may have few or many multiple notches at regular or irregular intervals. Plugs having smooth surfaces, however, are not considered wholly reliable for use in my invention, particularly in the larger sizes of rivets, because the force of the gas produced by the explosion may blow them out of the end of the shank of the rivet in spite of the constriction at the base of the rivet, because the gases find a ready path around the smooth-walled plug and thus expand the end of the shank sufficiently to permit the plug to escape. Even in those cases where smooth-surfaced plugs are not propelled from the rivet, the gases escape with sufiicient momentum to cause noise. When the surface is roughened, on the other hand, the constriction at the base of the plug embeds or infixes a portion of the plug, which is provided with projecting surfaces as a result of the roughness. Hence the gases from the explosion cannot find a ready path around the plug by which to rush out, thereby to cause noise and to expand the constriction and permit the plug to be forced out as a projectile.

I have found that the minimum shank reduction for satisfactory closure is about 15%, i. e., the opening is reduced to 85 of its original diameter. table illustrates various rivet shank diameters and diameters of the openings of typical rivets prepared in accordance with the present invention.

Normal Swaged end Percent reduction Shank Recess Plug Shank Open Shank Recess diameter, diameter, diameter, end end diamdiammches inches inches diameter, diameter, eter eter inches inches As will be noted from the foregoing table, the reduction in shank diameter is smaller proportionately than the reduction in the diameter of the opening. Obviously, the portion of the recess surrounding the plug will not be reduced beyond the smallest diameter of the plug, and, therefore, a measurement of shank reduction provides a more accurate measurement of the constriction applied to the rivet.

The largest diameter of the plug should be only slightly smaller than the normal inside diameter of the shank so that while it can be inserted with ease before the opening is constricted, it will become infixed in the inner wall of the shank by the constriction of the opening. To prevent improper insertion, it is preferred that the plug have a length greater than the normal inside diameter of the shank.

The constriction of the end of the rivet shank around the plug described may be accomplished in any manner desired. Both swaging and crimping equipment, for example, have produced satisfactory shank terminations for my rivets.

The following The production of my rivet closure is simple and in? expensive. Threads do not need to be tapped in the wall of the recess in the rivet, and the roughened surface does not have to be machined accurately. The roughened plug is simply inserted in the shank of the rivet after the explosive charge has been pressed in, and the end of the shank is compressed about the plug, as by the swaging or crimping procedures mentioned.

In addition to the advantage of noiselessness, the rivets of my invention have other advantages. The gases formed by the explosion of the explosive charges of the rivets are retained or leak out from the shank ends of rivets constructed in the manner described at such a slow rate that they do not blast nor cause corrosion of opposite structures, nor are any damaging metallic particles emitted by the explosion of the rivet. For example, when the noiseless rivets of my invention are used in the fabrication of refrigerators, insulating material in back of sheets to be riveted is not blown apart by a blast of gases or metal particles from the rivet. Furthermore, it is possible to use rivets of the noiseless type in structures of wood, which is readily split by the explosion of openshanked rivets because of the force of the blast.

An obstacle to the use of large explosive rivets of the prior art, in addition to the production of unbearable noise, is the fact that rivets of large size are subject to a jumping effect as a result of jet action when the charge is exploded. When rivets in accordance with my invention are used, however, the movement of the rivets is reduced appreciably.

Closures of the type described are advantageous not only in rivets of large diameter, but also in long rivets containing relatively large explosive charges, which commonly produce an inordinate amount of noise. The reduction in noise attained when smaller explosive rivets are provided with the closure of my invention is also beneficial, particularly in assembly-line work where large numbers of rivets are being fired simultaneously in one workroom.

The rivets of my invention have been described adequately in the foregoing, but it will be understood that many variations in form and materials may be made without departing from the spirit of my invention. I intend, therefore, to be limited only by the following claims.

I claim:

1. An explosive rivet having a shank member containing a longitudinal recess opening through a shank end, an explosive charge within said recess, and a metal plug having a diameter slightly less than the diameter of said recess entirely within said recess and adjacent to said explosive charge, said plug having a roughened surface, the opening of said recess in said shank being constricted to a diameter at least 15% less than the diameter of the unconstricted part of said recess whereby the recess wall at said opening overlies and engages said plug end, at least a portion of the roughened surface of said plug being infixed into the constricted wall of said recess.

2. An explosive rivet as claimed in claim 1, wherein said plug has a serrated surface.

3. An explosive rivet as claimed in claim 1, wherein said plug is a threaded cylinder.

4. An explosive rivet as claimed in claim 1, wherein said plug is a notched cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 943,233 Boyle Dec. 14, 1909 1,400,401 Allan Dec. 13, 1921 1,525,846 Wurtzebach Feb. 10, 1925 2,429,239 Rogers Oct. 21, 1947 FOREIGN PATENTS 89,450 Sweden June 8, 1937 

